Different approaches have been attempted to reduce vehicle fuel consumption in automotive vehicles. One approach has been to reduce the size of the internal combustion engine. Compared to a full sized engine, the smaller internal combustion engine uses less fuel. However, a smaller engine usually lacks the power associated with a larger engine.
Therefore, another trend has developed to use smaller internal combustion engines and to supplement those engines with devices that may provide additional power to the vehicle. In one example, one or more electric motors are used to supplement the smaller internal combustion engine. In this case, a power source for the electric motors, for example a battery, must be accommodated on the vehicle. However, batteries can be heavy, take up a significant amount of space and can be dangerous for people and for the environment to maintain and dispose of.
In another example, hydraulic accumulators can be used to supplement the power provided by a reduced size internal combustion engine. Fuel consumption and performance of a hydraulic hybrid system depend to a great extent on the control strategy used for operating the vehicle.